Herrera, 28, went 3-3 with a 4.25 ERA and 26 saves in 31 opportunities last season, when he was the team's closer for most of the year.

Karns' 2017 season, his first in Kansas City, ended when he was placed on the disabled list May 24 with nerve irritation in his pitching arm. Karns, 30, went 2-2 with a 4.17 ERA in nine appearances (eight starts) for the Royals.